Dishwasher and controlling method therefor

ABSTRACT

The present invention relates to a dishwasher for washing the dishes and the cooking utensils by spraying washing water, and a control method thereof. The control method of a dishwasher according to an embodiment of the present invention includes: a water supply step of opening a water supply valve to supply washing water to the sump; and a variable spray step of spraying the washing water by at least one of the plurality of spray arms by changing the number of revolutions of the washing pump stepwise, so that the washing water can be sprayed evenly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 and 35U.S.C. 365 to Korean Patent Application No. 10-2017-0177352, filed onDec. 21, 2017, which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a dishwasher and a control methodthereof, and more particularly, to a dishwasher for spraying washingwater to wash dishes or cooking utensils, and a control method thereof.

2. Description of the Related Art

A dishwasher is a household appliance for washing up dirt such as foodwastes on the dishes or cooking utensils (hereinafter, referred to as‘washing object’) by high-pressure washing water sprayed from a sprayarm.

The dishwasher generally includes a tub forming a washing chamber and asump mounted on the bottom of the tub to store washing water. Then, thewashing water is moved to the spray arm by the pumping operation of awashing pump installed inside the sump, and the washing water moved tothe spray arm is sprayed at high pressure through a spray hole formed inthe spray arm. Then, the washing water sprayed at a high pressureimpinges against the surface of the washing object, so that the dirt onthe washing object falls to the bottom of the tub.

Meanwhile, the dishwasher performs rinsing by spraying washing water tothe washing object so that residual dirt is removed. In this rinsingprocess, when performing a final rinsing of spraying the heated washingwater, any residual dirt should be removed as much as possible. Thus, itis required that the washing water is sprayed evenly onto the washingobject.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems, andprovides a dishwasher in which a spraying range of washing water variesduring rinsing, and a control method thereof.

In accordance with an aspect of the present invention, a method ofcontrolling a dishwasher includes: a water supply step of opening awater supply valve to supply washing water to the sump; and a variablespray step of spraying the washing water by at least one of theplurality of spray arms by changing the number of revolutions of thewashing pump stepwise, so that the washing water can be sprayed evenly.

In the variable spray step, the number of revolutions of the washingpump repeatedly decreases stepwise after increasing stepwise.

In the variable spray step, the number of steps in which the number ofrevolutions of the washing pump is increased is equal to the number ofsteps in which the number of revolutions is decreased.

In the variable spray step, a period in which the number of revolutionsof the washing pump is changed is constant.

Among the plurality of spray arms, a spray arm which sprays the washingwater is formed in a bar shape and rotates, and, in the variable spraystep, a period of change of the number of revolutions of the washingpump is equal to or larger than a maximum time during which the rotatingspray arm rotates once.

Among the plurality of spray arms, a spray arm which sprays the washingwater is formed in a bar shape and rotates, and in the variable spraystep, a period of change of the number of revolutions of the washingpump is equal to or larger than a time during which the rotating sprayarm rotates once at a minimum number of revolutions of the washing pump.

In the variable spray step, the washing pump has a constantincrease/decrease width for each step of the number of revolutions.

The plurality of spray arms comprises an upper spray arm which isdisposed at an intermediate portion of the tub and sprays the washingwater, and in the variable spray step, the washing pump pumps thewashing water to the upper spray arm.

The upper spray arm is formed in a bar shape and rotates, and in thevariable spray step, a rotation speed of the upper spray arm is changedstepwise.

In the variable spray step, a spray direction of the washing water ofthe upper spray arm is changed stepwise.

The number of revolutions of the washing pump in the variable spray stepis equal to or less than a maximum number of revolutions of the washingpump in the top spray step and is equal to or more than a maximum numberof revolutions of the washing pump in the lower spray step.

The method further includes an upper spray step of maintaining thenumber of revolutions of the washing pump uniformly, after the variablespray step; and a drain step of stopping an operation of the washingpump and draining the washing water stored in the sump to the outside,after the upper spray step.

In the upper spray step, the number of revolutions of the washing pumpmaintains an average value of the number of revolutions which is changedin the variable spray step.

The method further includes a heating step of heating the washing watersupplied to the sump, and, in the variable spray step, at least one ofthe plurality of spray arms sprays the heated washing water.

The water supply step, the heating step, and the variable spray step area heat rinsing process, and the method further includes, before the heatrinsing process is performed, a rinsing step of mixing the washing watersupplied from an external water source with a rinsing detergent, andspraying the mixed washing water by at least one of the plurality ofspray arms and then draining.

In accordance with another aspect of the present invention, a dishwasherincludes: a tub which accommodates a washing object; a plurality ofspray arms which spray washing water into the tub and are disposedvertically; a sump which stores the washing water; a washing pump whichpumps the washing water stored in the sump to at least one of theplurality of spray arms; and a controller which controls the washingpump and a heater, wherein the controller operates the heater andchanges the number of revolutions of the washing motor in a stepwisemanner to spray the washing water by at least one of the plurality ofspray arms.

The controller repeatedly decreases the number of revolutions of thewashing pump stepwise after increasing stepwise.

The controller changes the number of revolutions of the washing pumpperiodically.

The controller changes the number of revolutions of the washing pumpwith a constant increase/decrease width.

The dishwasher further includes a switching valve for selectivelyconnecting the washing pump with at least one of the plurality of sprayarms, wherein the plurality of spray arms includes an upper spray armdisposed at an intermediate portion of the tub and spraying washingwater, wherein the controller controls the switching valve to connectthe washing pump to the upper spray arm when the number of revolutionsof the washing motor is changed stepwise.

The dishwasher further includes a drain pump for draining the washingwater stored in the sump to the outside, wherein the controller changesthe number of revolutions of the washing motor in a stepwise manner andthen maintains uniformly, and stops an operation of the washing motorand then operates the drain pump. The dishwasher further includes aheater for heating the washing water sprayed by the plurality of sprayarms, wherein at least one of the plurality of spray arms sprays thewashing water heated by the heater.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will bemore apparent from the following detailed description in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a sectional view of a dishwasher according to an embodiment ofthe present invention;

FIG. 2 is a block diagram of a dishwasher according to an embodiment ofthe present invention;

FIG. 3 is a diagram illustrating each process in a general washingcourse of a dishwasher according to an embodiment of the presentinvention;

FIG. 4 is a diagram illustrating a control method during the heatrinsing of a dishwasher according to an embodiment of the presentinvention;

FIG. 5 is a diagram illustrating a control of the number of revolutionsof a washing pump in a control method of a dishwasher according to anembodiment of the present invention; and

FIG. 6 is a perspective view of an upper spray arm of a dishwasheraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described withreference to the accompanying drawings in detail. The same referencenumbers are used throughout the drawings to refer to the same or likeparts. Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the present invention.

Hereinafter, the present invention will be described with reference tothe drawings for explaining a dishwasher and a control method thereofaccording to embodiments of the present invention.

FIG. 1 is a sectional view of a dishwasher according to an embodiment ofthe present invention.

The dishwasher 1 according to an embodiment of the present inventionincludes a case 11 that forms an outer appearance, a tub 12 in which awashing object is accommodated, a door 20 that is provided on the frontsurface of the tub 12 and opens and closes the tub 12, a sump 100 thatis disposed below the tub 12 and stores washing water, a plurality ofspray arms 13, 14, 15 that spray washing water into the tub 12, a filter200 which filters the washing water which is sprayed from at least oneof the plurality of spray arms 13, 14, 15 and collected in the sump 100,a washing pump 150 that pumps washing water stored in the sump 100, anda switching valve 130 which flows the washing water pumped by thewashing pump 150 to at least one of the plurality of spray arms 13, 14,15.

The tub 11 is formed in a hexahedron shape having an opened frontsurface and forms a washing chamber 12 a therein. A communication hole12 c through which the washing water flows into the sump 100 is formedin a bottom 12 b of the tub 11. The washing chamber 12 a is providedwith a plurality of racks 16 and 17 for receiving the washing object.The plurality of racks 16 and 17 include a lower rack 16 disposed at alower portion of the washing chamber 12 a and an upper rack 17 disposedat an upper portion thereof. The lower rack 16 and the upper rack 17 arevertically spaced apart and can be slid forwardly of the tub 11 to bedrawn out.

The plurality of spray arms 13, 14, and 15 are disposed in the verticaldirection. The plurality of spray arms 13, 14, and 15 include a lowerspray arm 13 which is disposed in the lower end of the washing chamber12 a and sprays washing water from the lower side to the upper sidetoward the lower rack 16, an upper spray arm 14 which is disposed in amiddle portion of the height direction of the washing chamber 12 a thatis the upper side of the lower spray arm 13, and sprays washing waterfrom the lower side to the upper side toward the upper rack 17, and atop spray arm 15 which is disposed in the upper end of the washingchamber 12 a that is the upper side of the upper spray arm 14, andsprays washing water from the upper side to the lower side toward theupper rack 17.

The lower spray arm 13 is disposed below the lower rack 16, the upperspray arm 14 is disposed between the upper rack 17 and the lower rack16, and the top spray arm 15 is disposed above the upper rack 17.According to an embodiment, the upper spray arm 14 may spray downwardtoward the lower rack 16, and spray upwardly and downwardly toward boththe upper rack 17 and the lower rack 16.

Each of the lower spray arm 13 and the upper spray arm 14 rotates aboutthe center of a bar in the form of a bar. Each of the lower spray arm 13and the upper spray arm 14 rotates by the supply of washing water. Eachof the lower spray arm 13 and the upper spray arm 14 is provided with anozzle (not shown) on the upper surface of the bar.

The plurality of spray arms 13, 14, and 15 are supplied with the washingwater from the washing pump 150 through a plurality of spray armconnecting flow paths 18, 19, and 21. The plurality of spray armconnecting flow paths 18, 19, and 21 include a lower spray armconnecting flow path 18 connected to the lower spray arm 13, an upperspray arm connecting flow path 19 connected to the upper spray arm 14,and a top spray arm connecting flow path 21 connected to the top sprayarm 15.

The lower spray arm 13, the upper spray arm 14, and the top spray arm 15are supplied with the washing water from the washing pump 150 throughthe lower spray arm connecting flow path 18, the upper spray armconnecting flow path 19, and the top spray arm connecting flow path 21.

The sump 100 is disposed below the bottom 12 b of the tub 12 to collectwashing water. The sump 100 is connected to a water supply flow path 23through which washing water supplied from an external water sourceflows. The water supply flow path 23 is provided with a water supplyvalve 22 for controlling washing water supplied from the external watersource. When the water supply valve 22 is opened, the washing watersupplied from the external water source flows into the sump 100 throughthe water supply flow path 23.

The sump 100 is connected to a drain flow path 24 for guiding the storedwashing water to the outside of the dishwasher 1. The drain flow path 24is provided with a drain pump 25 for draining the washing water in thesump 100 through the drain flow path 24. The drain pump 25 includes adrain motor (not shown) for generating a rotational force. When thedrain pump 25 is operated, the washing water stored in the sump 100flows to the outside of the case 11 through the drain flow path 24.

A filter 26 is installed in the communication hole 12 c to filter thedirt from the washing water moving from the tub 12 to the sump 100. Inthe filter 200, a lower portion where mesh is formed is inserted intothe sump 100, and an opened upper portion protrudes to the upper side ofthe tub 12. The washing water sprayed through the plurality of sprayarms 13, 14, 15 falls to the bottom 12 b of the tub 12 together with thedirt on the washing object. The washing water flowing on the bottom 12 bof the tub 12 flows into the upper portion of the filter 200, passesthrough the mesh of lower portion, and is stored in the sump 100 afterbeing filtered. The level of the washing water stored in the sump 100needs to be maintained above the lower end of the filter 200, in orderfor filtration of the filter 200 to be smoothly performed.

The switching valve 130 selectively supplies the washing water pumped bythe washing pump 150 to at least one of the lower spray arm 13, theupper spray arm 14, and the top spray arm 15. The switching valve 130selectively connects a washing water supply path 180 and at least one ofthe plurality of spray arm connecting flow paths 18, 19 and 21.

The washing pump 150 supplies washing water stored in the sump 100 to atleast one of the plurality of spray arms 13, 14, 15. The washing pump150 includes a washing motor 157 that generates a rotational force andan impeller 155 that is rotated by the washing motor 157 to pump thewashing water. The washing motor 157 is a motor whose RPM can be varied,and a change of the number of revolutions of the washing pump 150 (thenumber of revolutions per time) means a change of the RPM of the washingmotor 157. The number of revolutions of the washing pump 150 can bemaintained or the number of revolutions of the washing pump 150 can bechanged during operation. The number of revolutions of the washing pump150 is proportional to the flow rate of the washing water that is pumpedby the washing pump 150. When the number of revolutions of the washingpump 150 is changed, the spray direction of the washing water sprayedfrom at least one of the plurality of spray arms 13, 14, 15 connected tothe washing pump 150 is changed. When the washing pump 150 is connectedto at least one of the lower spray arm 13 and the upper spray arm 14, ifthe number of revolutions of the washing pump 150 is changed, therotation speed of the lower spray arm 13 and/or the upper spray arm 14is changed.

The washing pump 150 is connected to the sump 100 and a water collectingpath 170. The washing pump 150 is connected to the switching valve 130and the washing water supply path 180. When the washing pump 150 isoperated, the washing water stored in the sump 100 flows into thewashing pump 150 through the water collecting path 170 and then ispumped to the switching valve 130 through the washing water supply path180. Since the water collecting path 170 is connected to the lateralside of the washing pump 150, it is necessary that the level of thewashing water stored in the sump 100 is maintained above a connectionportion of the water collecting path 170 in order for the washing waterto flow into the washing pump 150 during operation of the washing pump150.

The heater 140 is coupled to the lower side of the washing pump 150 toheat the washing water in the washing pump 150. The heater 140 generateshot water by heating the washing water flowing in the washing pump 150when the washing pump 150 operates. The washing water heated by theheater 140 is sprayed into the tub 12 through at least one of theplurality of spray arms 13, 14 and 15. According to an embodiment, theheater 140 may be disposed within the sump 100.

FIG. 2 is a block diagram of a dishwasher according to an embodiment ofthe present invention, and FIG. 3 is a diagram illustrating each processin a general washing course of a dishwasher according to an embodimentof the present invention.

The controller 29 controls the water supply valve 22, the washing pump150, the drain pump 25, the switching valve 130, and the heater 140 toperform washing on the washing object. The controller 29 performs eachprocess according to the washing course selected by the user.

The controller 29 sequentially performs a preliminary washing 1 P310, apreliminary washing 2 P320, a preliminary washing 3 P330, a main washingP340, a rinsing P350, and a heat rinsing P360.

The plurality of preliminary washings P310, P320, P330 is a process forspraying washing water on the washing object to remove dirt attached tothe washing object. In each of the plurality of preliminary washingsP310, P320, P330, the controller 29 controls the water supply valve 22to supply the washing water from an external water source into the sump100. After the water supply, the controller 29 operates the washing pump150 to pump the washing water in the sump 100 and controls the switchingvalve 130 to spray washing water through at least one of the pluralityof spray arms 13. The washing water sprayed through at least one of theplurality of spray arms 13, 14, 15 drops the dirt attached to thewashing object onto the bottom 12 b of the tub 12 so that the dirt canbe collected by the filter 26. After spraying the washing water, thecontroller 29 operates the drain pump 25 to drain the washing water inthe sump 100 to the outside.

In the present embodiment, it is illustrated that the preliminarywashing P310, P320, P330 is performed three times. However, according toan embodiment, it may be performed various times, e.g., once or more.

The main washing P340 is a process for spraying heated washing wateronto the washing object so as to heat the washing object, and removingthe dirt attached to the washing object. The controller 29 controls thewater supply valve 22 to supply the washing water from an external watersource to the sump 100, controls the heater 140 to heat the washingwater, operates the washing pump 150 to spray the heated washing waterthrough at least one of the plurality of spray arms 13, 14, 15, andoperates the drain pump 25 to drain the washing water in the sump 100 tothe outside. During the main washing P340, the washing detergent may bemixed with the washing water.

The rinsing P350 is a process for removing residual dirt attached to thewashing object. In the rinsing process P350, the controller 29 controlsthe water supply valve 22 to supply the washing water from an externalwater source to the sump 100, operates the washing pump 150 to spray thewashing water through at least one of the plurality of spray arms 13,14, 15, and operates the drain pump 25 to drain the washing water in thesump 100 to the outside. During the rinsing P350, the rinsing detergentmay be mixed with the washing water.

The heat rinsing P360 is a process for heating the washing object byspraying the heated washing water onto the washing object, and finallyremoving the residual dirt attached to the washing object. In the heatrinsing process P360, the controller 29 controls the water supply valve22 to supply the washing water from the external water source to thesump 100, controls the heater 140 to heat the washing water, operatesthe washing pump 150 to spray the heated washing water through at leastone of the plurality of spray arms 13, 14, 15, and operates the drainpump 25 to drain the washing water in the sump 100 to the outside.

FIG. 4 is a diagram illustrating a control method during the heatrinsing of a dishwasher according to an embodiment of the presentinvention.

The controller 29 performs water supply P361 of the heat rinsing P360.The controller 29 controls the water supply valve 22 to supply the sump100 with washing water from an external water source. When thecontroller 29 opens the water supply valve 22, the washing watersupplied from the external water source flows into the sump 100 throughthe water supply flow path 23. The controller 29 controls the watersupply valve 22 such that the level of the washing water supplied to thesump 100 at the maximum rotation speed of the washing pump 150 is equalto or higher than the water level (filterable water level) at which thefiltration of the dirt can be smoothly performed in the filter 200 andthe water level (washing water circulatable level) at which the washingwater can be flowed by the washing pump 150. The controller 29 closesthe water supply valve 22 and terminates the water supply P361 when thewashing water is supplied to a target water level.

When the water supply P361 is completed, the controller 29 performs afirst top spray P362. In the first top spray P362, the controller 29operates the heater 140 to heat the washing water. In addition, thecontroller 29 controls the switching valve 130 to connect the washingwater supply path 180 and the top spray arm connecting flow path 21 sothat the washing pump 150 is connected to the top spray arm 15. Thecontroller 29 operates the washing pump 150 to pump the washing waterstored in the sump 100 to the top spray arm 15. The controller 29 spraysthe heated washing water through the top spray arm 15 downward towardthe upper rack 17.

The controller 29 gradually increases the rotation speed of the washingpump 150 until the level of the washing water supplied to the sump 100in the first top spray P362 is lowered to reach the filterable waterlevel and the washing water circulatable level (the highest targetrotation speed). When the number of revolutions of the washing pump 150reaches the maximum target number of revolutions, the controller 29maintains this number of revolutions for a predetermined time and thencompletes the first top spray P362.

When the first top spray P362 is completed, the controller 29 performs afirst lower spray P363. In the first lower spray P363, the controller 29continuously operates the heater 140, and controls the switching valve130 to connect the washing water supply path 180 and the lower spray armconnecting flow path 18 so that the washing pump 150 is connected to thelower spray arm 13. The controller 29 lowers the number of revolutionsof the washing pump 150 to the extent that the washing water can besprayed through the lower spray arm 13 (the minimum target number ofrevolutions). The controller 29 operates the washing pump 150 withoutstopping after the first top spray P362 while reducing only the numberof revolutions of the washing pump 150 so that the washing water storedin the sump 100 is pumped to the lower sandstone 13. The controller 29sprays the heated washing water through the lower spray arm 13 upwardlytoward the lower rack 16.

When the number of revolutions of the washing pump 150 reaches theminimum target number of revolutions, the controller 29 maintains thisnumber of revolutions for a predetermined time and temporarily stops theoperation of the washing pump 150, operates the washing pump 150 again,and controls the number of revolutions of the washing pump 150 to be theminimum target number of revolutions. When the number of revolutions ofthe washing pump 150 reaches the minimum target number of revolutions,the controller 29 maintains this number of revolutions for apredetermined time and then terminates the first lower spray P363.

When the first lower spray P363 is completed, the controller 29 performsa first variable spray P364. In the first variable spray P364, thecontroller 29 continuously operates the heater 140, and controls theswitching valve 130 to connect the washing water supply path 180 and theupper spray arm connecting flow path so that the washing pump 150 isconnected to the upper spray arm 14. The controller 29 changes thenumber of revolutions of the washing pump 150 in a stepwise manner. Inthe first variable spray P364, the controller 29 repeats the stepwisedecrease of the number of revolutions of the washing pump 150 after astepwise increase. In the first variable spray P364, when the controller29 changes the number of revolutions of the washing pump 150 in astepwise manner, the number of revolutions of the upper spray arm 14 ischanged in a stepwise manner, and the spray direction of the washingwater is also changed in a stepwise manner.

The controller 29 changes the number of revolutions of the washing pump150 to be equal to or lower than the maximum target number ofrevolutions of the washing pump 150 in the first top spray P362 and tobe equal to or higher than the minimum target number of revolutions ofthe washing pump 150 in the first lower spray (P363). The controller 29controls the number of revolutions of the washing pump 150 to varybetween the maximum number of revolutions of the washing pump 150 in thefirst top spray P362 and the maximum number of revolutions of thewashing pump 150 in the first lower spray P363.

A detailed description of the first variable spray P364 will be givenlater with reference to FIG. 5 and the following.

The controller 29 changes only the number of revolutions of the washingpump 150 and operates the washing pump 150 without stopping after thefirst lower spray P363 so that the washing water stored in the sump 100is pumped to the upper spray arm 14. The controller 29 sprays the heatedwashing water through the upper spray arm 14 upwardly toward the upperrack 17. The controller 29 changes the number of revolutions of thewashing pump 150 in a stepwise manner for a predetermined time and thenterminates the first variable spray P364.

When the first variable spray P364 is completed, the controller 29performs a second top spray P365. In the second top spray P365,similarly to the first top spray P362, the controller 29 continuouslyoperates the heater 140 and controls the switching valve 130 such thatthe washing pump 150 is connected to the top spray arm 15 and the numberof revolutions of the washing pump 150 is increased to the maximumtarget number of revolutions.

When the second top spray P365 is completed, the controller 29 performsthe second lower spray P366. In the second lower spray P366, similarlyto the second lower spray P366, the controller 29 continuously operatesthe heater 140 and controls the switching valve 130 to connect thewashing pump 150 to the lower spray arm 13, and reduces the number ofrevolutions of the washing pump 150 to the minimum target number ofrevolutions. In the second lower spray P366, the controller 29temporarily stops the operation of the washing pump 150 in the middle ofmaintaining the minimum target number of revolutions of the washing pump150.

When the second lower spray P366 is completed, the controller 29performs a second variable spray P367. In the second variable sprayP367, similarly to the first variable spray P364, the controller 29continuously operates the heater 140 and controls the switching valve130 to connect the washing pump 150 to the upper spray arm 14, andchanges the number of revolutions of the washing pump 150 in a stepwisemanner.

When the second variable spray P367 is completed, the controller 29performs an upper spray P368. In the upper spray P368, the controller 29stops the operation of the heater 140 and terminates the heating of thewashing water. The stop of the operation of the heater 140 may beaccomplished at the beginning or at the end of the upper spray P368. Inthe upper spray P368, the controller 29 maintains the switching valve130 to connect the washing pump 150 and the upper spray arm 14 after thesecond variable spray P367. In the upper spray P368, the controller 29operates the washing pump 150 without stopping after the second variablespray P367, but maintains the number of revolutions of the washing pump150 uniformly. The controller 29 controls the number of revolutions ofthe washing pump 150 to be the average value (or the intermediate valuebetween the maximum number of revolutions and the minimum number ofrevolutions) of the number of revolutions of the washing pump 150 in thesecond variable spray P367 (or in the first variable spray P364) andthen maintains this number of revolutions. In the upper spray P368, thecontroller 29 maintains the number of revolutions of the washing pump150 so that the filterable water level, the washing water circulatablewater level, and the washing water spray flow amount through the upperspray P368 can be ensured, and collects dirt into the filter 200 andcollects washing water into the sump 100. The controller 29 maintainsthe number of revolutions of the washing pump 150 for a predeterminedtime, and then stops the operation of the washing pump 150 to terminatethe upper spray P368.

When the upper spray P368 is completed, the controller 29 performs adrain (P369). The controller 29 operates the drain pump 25 to drain thewashing water stored in the sump 100 to the outside. When the controller29 operates the drain pump 25, the washing water stored in the sump 100flows to the outside of the case 11 through the drain flow path 24. Whenall of the washing water stored in the sump 100 is drained, thecontroller 29 stops the operation of the drain pump 25 and terminatesthe heat rinsing P360.

In the above-described embodiment, the second top spray P365, the secondlow spray P366, and the second variable spray P367 may be omitted. Inthis case, after the first variable spray P364, the upper spray P368,and the drain P369 may be performed sequentially.

In the embodiment described above, it is illustrated that the upperspray arm 14 sprays the washing water in the steps of the first variablespray P364 and the second variable spray P367. However, according to anembodiment, the lower spray arm 13 may spray the washing water.

FIG. 5 is a diagram illustrating a control of the number of revolutionsof a washing pump in a control method of a dishwasher according to anembodiment of the present invention, and FIG. 6 is a perspective view ofan upper spray arm of a dishwasher according to an embodiment of thepresent invention.

FIG. 5 shows the number of revolutions of the washing pump 150 dependingon time in the first variable spray P364 and the second variable sprayP367. In FIG. 5, x denotes a period in which the number of revolutionsof the washing pump 150 is changed, and y denotes a stepwiseincrease/decrease width in which the number of revolutions of thecleaning pump 150 is changed. yz denotes the total increase/decreasewidth of the change in the number of revolutions of the washing pump150. z denotes the number of the increasing and decreasing steps of thenumber of revolutions of the washing pump 150.

It is preferable that the period x of change of the number ofrevolutions of the washing pump 150 is equal to or larger than a maximumtime during which the upper spray arm 14 rotates once. The rotationspeed w of the upper spray arm 14 is changed according to the number ofrevolutions the washing pump 150, and the rotation speed w of the upperspray arm 14 becomes the lowest when the number of revolutions of thewashing pump 150 is the lowest. The time for one rotation of the upperspray arm 14 becomes the maximum when the rotation speed w of the upperspray arm 14 is the lowest. It is preferable that the period x of changeof the number of revolutions is equal to or larger than the time of onerevolution at the minimum number of revolutions of the washing pump 150.

The period x of change of the number of revolutions of the washing pump150 is equal to the period of time during which the number ofrevolutions of the washing pump 150 is maintained. Since the spraydirection of the washing water sprayed from a nozzle 14 a of the upperspray arm 14 is maintained uniformly when the number of revolutions ofthe washing pump 150 is maintained, the upper spray arm 14 is rotated atleast one revolution in the same spray direction so that the washingwater is uniformly sprayed on the horizontal plane. In the presentembodiment, the period x of change of the number of revolutions of thewashing pump 150 is 5 seconds.

The spray direction of the washing water may be evenly changed during astepwise change in which the number of revolutions of the washing pump150 is maintained uniformly and then rapidly changed and maintaineduniformly again. The spray direction of the washing water is related notonly to the opening direction of the nozzle 14 a and the flow rate ofwashing water depending on the number of revolutions of the washing pump150 but also to the rotation speed of the upper spray arm 14. Accordingto such a complex factor, the inventors of the present invention haveexperimentally found that the spray direction of the washing water ischanged evenly to be evenly applied to the washing object, when thenumber of revolutions of the washing pump 150 is changed to the period xof change of the number of revolutions of the washing pump 150 in astepwise manner in comparison with the case where the number ofrevolutions of the washing pump 150 is gradually changed linearly orcurvedly.

The washing pump 150 repeats the stepwise decrease in the number ofrevolutions after the stepwise increase. The number z of steps ofincreasing the number of revolutions of the washing pump 150 ispreferably equal to the number z of steps of decreasing the number ofrevolutions. It is preferable that the number z of steps of increasingor decreasing the number of revolutions is an even number such that thenumber of revolutions of the washing pump 150 is maintained for theperiod x of change at the average value (intermediate value between themaximum number of revolutions and the minimum number of revolutions) forthe number of revolutions of the washing pump 150.

It is preferable that all the increase/decrease width y of each step isconstant when the number of revolutions of the washing pump 150 isincreased and decreased. It is preferable that the totalincrease/decrease width yz of the change in the number of revolutions ofthe washing pump 150 is constant when the number of revolutions of thewashing pump 150 is repeatedly increased or decreased in a stepwisemanner. In the present embodiment, the number z of steps for increasingor decreasing the number of revolutions is 4, and the increase/decreasewidth y for each step is 200 RPM. Accordingly, in the presentembodiment, the total increase/decrease width yz is 800 RPM.

The inventors of the present invention have experimentally found thatwhen the number of revolutions of the washing pump 150 is changedun-uniformly in a stepwise manner, the water level drops sharply so thatthe filterable water level and the washing water circulatable waterlevel are not ensured or the washing water is not sprayed through thenozzle 14 a. However, as described above, it has been found that whenthe number of revolutions of the washing pump 150 is changed uniformlyin a stepwise manner by making the increase/decrease width y for eachstep to be equal to the number z of steps of increase, the washing wateris continuously sprayed through the nozzle 14 a while ensuring thefilterable water level and the washing water circulatable water level.

According to the dishwasher of the present invention and the controlmethod thereof, one or more of the following effects can be obtained.

First, the number of revolutions of the washing pump that pumps thewashing water to the spray arm is varied stepwise so that the sprayrange of the washing water can be varied stepwise, thereby uniformlyspraying the washing water to the washing object.

Second, the number of revolutions of the washing pump can be varied inthe same period and in the same increase/decrease width, therebyensuring the filterable water level and the washing water circulatablewater level.

Third, the number of revolutions of the washing pump is changed, but thenumber of revolutions is maintained while the washing arm rotates atleast once, so that the washing arm can rotate at least once in acertain washing water spray direction.

Fourth, the rinsing performance can be improved by repeatedly increasingand decreasing the number of revolutions of the washing pump in astepwise manner between the spray pressure at which the washing water issprayed to the washing arm and the spray pressure at which the lowestwater level can be ensured.

Fifth, the number of revolutions of the washing pump is changed stepwiseand then the number of revolutions is kept constant, thereby collectingthe dirt in the filter before draining, and collecting the washing waterstably in the sump.

Sixth, the washing water is sprayed evenly onto the washing object in afinal process in which the heated washing water is sprayed, therebycompletely removing the residual dirt in the washing object.

Hereinabove, although the present invention has been described withreference to exemplary embodiments and the accompanying drawings, thepresent invention is not limited thereto, but may be variously modifiedand altered by those skilled in the art to which the present inventionpertains without departing from the spirit and scope of the presentinvention claimed in the following claims.

What is claimed is:
 1. A method of controlling a dishwasher thatincludes a tub configured to receive a washing object, a plurality ofspray arms configured to spray washing water to the tub, a sumpconfigured to store washing water, and a washing pump configured to pumpwashing water stored in the sump to the plurality of spray arms, themethod comprising: supplying washing water by opening a water supplyvalve of the dishwasher; and spraying washing water through at least oneof the plurality of spray arms based on changing a number of revolutionsof the washing pump by one or more levels.
 2. The method of claim 1,wherein changing the number of revolutions of the washing pump comprisesincreasing the number of revolutions of the washing pump by one or moreincrement levels and decreasing the number of revolutions of the washingpump in one or more decrement levels, and wherein decreasing the numberof revolutions of the washing pump comprises repeatedly decreasing thenumber of revolutions of the washing pump in the one or more decrementlevels after increasing the number of revolutions of the washing pump bythe one or more increment levels.
 3. The method of claim 2, wherein anumber of the one or more decrement levels is equal to a number of theone or more increment levels.
 4. The method of claim 1, wherein changingthe number of revolutions of the washing pump comprises maintaining thenumber of revolutions of the washing pump for a constant period at eachlevel of the one or more levels.
 5. The method of claim 4, wherein theplurality of spray arms comprises a first spray arm that has a bar shapeand that is configured to rotate, and wherein maintaining the number ofrevolutions of the washing pump for the constant period comprisesmaintaining the number of revolutions of the washing pump for a durationthat is greater than or equal to a maximum time period during which thefirst spray arm rotates once.
 6. The method of claim 4, wherein theplurality of spray arms comprises a first spray arm that has a bar shapeand that is configured to rotate and spray washing water, and whereinmaintaining the number of revolutions of the washing pump for theconstant period comprises maintaining the number of revolutions of thewashing pump for a duration that is greater than or equal to a rotationperiod corresponding to one rotation of the first spray arm at a minimumnumber of revolutions of the washing pump.
 7. The method of claim 1,wherein changing the number of revolutions of the washing pump by theone or more levels comprises: increasing the number of revolutions ofthe washing pump by a step width corresponding to a difference in thenumber of revolutions between two adjacent levels among a plurality oflevels; and decreasing the number of revolutions of the washing pump bythe step width.
 8. The method of claim 1, wherein the plurality of sprayarms comprises an upper spray arm disposed at the tub, and whereinspraying washing water through at least one of the plurality of sprayarms comprises supplying, by the washing pump, washing water to theupper spray arm.
 9. The method of claim 8, wherein the upper spray armhas a bar shape and is configured to rotate, and wherein sprayingwashing water comprises spraying washing water based on changing arotation speed of the upper spray arm by one or more speed steps. 10.The method of claim 8, wherein spraying washing water comprises sprayingwashing water based on changing a spray direction of washing watersprayed from the upper spray arm in one or more direction steps.
 11. Themethod of claim 8, further comprising: supplying, by operating thewashing pump, washing water stored in the sump to a top spray arm amongthe plurality of spray arms, the top spry arm being disposed at an upperportion of the tub and being configured to spray washing water in adownward direction; and supplying, by operating the washing pump,washing water stored in the sump to a lower spray arm among theplurality of spray arms, the lower spray arm being disposed at a lowerportion of the tub and being configured to spray washing water in anupward direction, and wherein changing the number of revolutions of thewashing pump comprises changing the number of revolutions of the washingpump to a range (i) that is less than or equal to a maximum number ofrevolutions of the washing pump at which the washing pump operates tosupply washing water to the top spray arm and (ii) that is greater thanor equal to a maximum number of revolutions of the washing pump at whichthe washing pump operates to supply washing water to the lower sprayarm.
 12. The method of claim 1, further comprising: maintaining thenumber of revolutions of the washing pump after changing the number ofrevolutions of the washing pump; and stopping operation of the washingpump and draining washing water stored in the sump to an outside of thesump after maintaining the number of revolutions of the washing pump.13. The method of claim 12, wherein maintaining the number ofrevolutions of the washing pump comprises maintaining the number ofrevolutions of the washing pump at an average value of the number ofrevolutions of the washing pump of the one or more levels.
 14. Themethod of claim 1, further comprising heating washing water supplied tothe sump, wherein spraying washing water comprises spraying heatedwashing water through at least one of the plurality of spray arms. 15.The method of claim 14, further comprising: mixing washing watersupplied from an external water source with a rinsing detergent;spraying the mixed washing water through at least one of the pluralityof spray arms and then draining the mixed washing water; and based onspraying the mixed washing water and draining the mixed washing water,performing a heat rinsing process that comprises supplying washing waterto the sump, heating washing water supplied to the sump, and sprayingheated washing water through at least one of the plurality of spray armsbased on changing the number of revolutions of the washing pump by theone or more levels.
 16. A dishwasher comprising: a tub configured toaccommodate a washing object; a plurality of spray arms that arearranged at one or more vertical positions in the tub and that areconfigured to spray washing water into the tub; a sump configured tostore washing water; a washing pump configured to supply washing waterstored in the sump to at least one of the plurality of spray arms, thewashing pump comprising a washing motor; a heater configured to heatwashing water supplied to the sump; and a controller configured tocontrol the washing pump and the heater, wherein the controller isconfigured to, based on operating the heater and changing a number ofrevolutions of the washing motor by one or more levels, spray washingwater through at least one of the plurality of spray arms.
 17. Thedishwasher of claim 16, wherein the controller is further configured torepeatedly decrease the number of revolutions of the washing pump by oneor more decrement levels after increasing the number of revolutions ofthe washing pump by one or more increment levels.
 18. The dishwasher ofclaim 16, wherein the controller is configured to change the number ofrevolutions of the washing pump by a constant step width correspondingto a difference in the number of revolutions between two adjacent levelsamong a plurality of levels.
 19. The dishwasher of claim 16, furthercomprising a switching valve configured to selectively connect thewashing pump to at least one of the plurality of spray arms, wherein theplurality of spray arms comprise an upper spray arm disposed at anintermediate portion of the tub, and wherein the controller is furtherconfigured to control the switching valve to connect the washing pump tothe upper spray arm based on changing the number of revolutions of thewashing motor in the one or more levels.
 20. The dishwasher of claim 16,further comprising a drain pump configured to drain washing water storedin the sump to an outside of the sump, wherein the controller isconfigured to: change the number of revolutions of the washing motor inthe one or more levels and then maintain the number of revolutions ofthe washing motor, and stop operation of the washing motor and thenoperate the drain pump.